Table 2.

Confidence Levels

	Pathologic evidence	Clinician assessment	Treatment for acute GVHD	Comments
Confirmed	Unequivocal pathologic evidence of GVHD	GVHD is the etiology for symptoms	Not applicable	GVHD is clearly present even if other etiologies may co-exist simultaneously
Probable	Not required	GVHD most likely etiology for symptoms (as evidenced by treatment being provided)	Yes	GVHD is most likely present but other etiologies may also explain the symptoms and there insufficient evidence to make a confirmed diagnosis
Possible	Not required	GVHD in differential diagnosis (but no treatment is being provided)	No	GVHD may be present, but other etiologies are favored to the degree that GVHD treatment is not initiated
Negative	Unequivocal evidence of a diagnosis other than GVHD (e.g., drug rash)	GVHD is not considered as an explanation for the symptoms	No and the symptoms resolve without GVHD treatment	A “negative” biopsy (e.g., normal skin) is not unequivocal evidence of a diagnosis other than GVHD